The present invention relates to spin coating apparatus used to coat a photoresist on a semiconductor wafer substrate in the fabrication of semiconductor integrated circuits. More particularly, the present invention relates to a new and improved gas purge arm which facilitates a diffuse spray pattern of nitrogen purge gas against a substrate surface after a photoresist coating process in a spin coating apparatus.
The fabrication of various solid state devices requires the use of planar substrates, or semiconductor wafers, on which integrated circuits are fabricated. The final number, or yield, of functional integrated circuits on a wafer at the end of the IC fabrication process is of utmost importance to semiconductor manufacturers, and increasing the yield of circuits on the wafer is the main goal of semiconductor fabrication. After packaging, the circuits on the wafers are tested, wherein non-functional dies are marked using an inking process and the functional dies on the wafer are separated and sold. IC fabricators increase the yield of dies on a wafer by exploiting economies of scale. Over 1000 dies may be formed on a single wafer which measures from six to twelve inches in diameter.
Various processing steps are used to fabricate integrated circuits on a semiconductor wafer. These steps include deposition of a conducting layer on the silicon wafer substrate; formation of a photoresist or other mask such as titanium oxide or silicon oxide, in the form of the desired metal interconnection pattern, using standard lithographic or photolithographic techniques; subjecting the wafer substrate to a dry etching process to remove the conducting layer from the areas not covered by the mask, thereby etching the conducting layer in the form of the masked pattern on the substrate; removing or stripping the mask layer from the substrate typically using reactive plasma and chlorine gas, thereby exposing the top surface of the conductive interconnect layer; and cooling and drying the wafer substrate by applying water and nitrogen gas to the wafer substrate.
The numerous processing steps outlined above are used to cumulatively apply multiple electrically conductive and insulative layers on the wafer and pattern the layers to form the circuits. The final yield of functional circuits on the wafer depends on proper application of each layer during the process steps. Proper application of those layers depends, in turn, on coating the material in a uniform spread over the surface of the wafer in an economical and efficient manner.
During the photolithography step of semiconductor production, light energy is applied through a reticle mask onto a photoresist material previously deposited on the wafer to define circuit patterns which will be etched in a subsequent processing step to define the-circuits on the wafer. Because these circuit patterns on the photoresist represent a two-dimensional configuration of the circuit to be fabricated on the wafer, minimization of particle generation and uniform application of the photoresist material to the wafer are very important. By minimizing or eliminating particle generation during photoresist application, the resolution of the circuit patterns, as well as circuit pattern density, is increased.
Photoresist materials are coated onto the surface of a wafer by dispensing a photoresist fluid typically on the center of the wafer as the wafer rotates at high speeds within a stationary bowl or coater cup of a spin coating apparatus. The coater cup catches excess fluids and particles ejected from the rotating wafer during application of the photoresist. The photoresist fluid dispensed onto the center of the wafer is spread outwardly toward the edges of the wafer by surface tension generated by the centrifugal force of the rotating wafer. This facilitates uniform application of the liquid photoresist on the entire surface of the wafer.
Spin coating of photoresist on wafers is carried out in an automated track system using wafer handling equipment which transport the wafers between the various photolithography operation stations, such as vapor prime resist spin coat, develop, baking and chilling stations. Robotic handling of the wafers minimizes particle generation and wafer damage. Automated wafer tracks enable various processing operations to be carried out simultaneously. Two types of automated track systems widely used in the industry are the TEL (Tokyo Electron Limited) track and the SVG (Silicon Valley Group) track.
A typical conventional spin coating apparatus for coating semiconductor wafers with a photoresist liquid is generally indicated by reference numeral 8 in FIGS. 1 and 2. The spin coating apparatus 8 includes a coater cup 3 which includes a top opening 6 and partially encloses a wafer support stage or chuck 1 on which is supported the wafer 2. A chemical dispensing system 10 includes a nitrogen gas spray arm 12, an acid dispensing arm 13 and a deionized (DI) water spray arm 14, each of which extends from a corresponding arm slot 7 in an arm mount 11. As shown in FIG. 2, each of the arms 12, 13, 14 is capable of swinging or pivoting from a stored position on the side of the coater cup 3, over the top of the coater cup 3 for dispensing the corresponding liquid through the top opening 6 onto the wafer 2. In operation, the chuck 1 rotates the wafer 2 at high speeds, typically as high as 4,000 rpm, either after or as the liquid photoresist (not shown) is dispensed onto the center of the spinning wafer 2, through the top opening 6. By operation of centrifugal force imparted to the wafer 2 by the rotating chuck 1, the dispensed photoresist liquid is spread across and uniformly coated on the surface of the wafer 2. Exhaust solvent gases and photoresist particles generated during the process are vented from the coater cup 3 through an exhaust pipe 4 which may be connected to an exhaust manifold 5.
After the liquid photoresist is applied to the wafer 2, the acid dispensing arm 13 sweeps over the center of the coater cup 3 and back to the xe2x80x9chomexe2x80x9d position on the side of the coater cup 3 as acid is dispensed from the arm 13 through the top opening 6 onto the surface of the spinning wafer 2 at a pressure of typically about 0.3 psi. This step removes excess photoresist, as well as photoresist particles, from the wafer 2. Next, the water spray arm 14 sweeps over the center of the coater cup 3 and back to the xe2x80x9chomexe2x80x9d position on the side of the coater cup 3 to spray DI water, at a pressure of typically about 20-40 psi, through the top opening 6 and onto the wafer 2 to remove residual acid from the wafer 2. Finally, the nitrogen gas spray arm 12 is initially positioned over the center of the coater cup 3 and then sweeps back to the xe2x80x9chomexe2x80x9d position on the side of the coater cup 3 to blow nitrogen gas, at a pressure of typically about 15 psi, onto the surface of the spinning wafer 2. This final step dries most of the DI water remaining on the wafer 2.
As shown in FIG. 3, the nitrogen spray arm 12 includes a central dispensing tube 15 that terminates in a nozzle opening 16 at the end of the nitrogen spray arm 12. The nozzle opening 16 typically has a relatively small diameter of about 1.0 mm to about 1.5 mm, and this tends to eject the nitrogen gas onto the surface of the wafer 2 in a narrow, forceful stream 18. The nitrogen gas stream 18 tends to blow or splash water droplets 17 from localized areas on the surface of the wafer 2 contacted directly by the nitrogen gas stream 18 while spreading the water droplets 17 to adjacent areas on the wafer 2. Consequently, some of the water droplets 17 remain on the wafer 2, forming chemical and water spots on the surface of the wafer 2 after the cleaning process. Chemical and water spots remaining on the wafer 2 after the photoresist application process tend to adversely affect device performance and reduce the yield of devices on the wafer 2.
An object of the present invention is to provide a gas spray arm which is capable of applying a drying gas in a diffuse pattern to the surface of a substrate.
Another object of the present invention is to provide a gas spray arm which is effective in drying water and chemicals from a substrate.
Still another object of the present invention is to provide a gas spray arm for preventing the formation of water or chemical spots on a substrate after a process is carried out on the substrate typically in a spin coating apparatus.
Another object of the present invention is to provide a multi-nozzle gas spray arm which includes at least two spray arms for ejecting a gas, particularly nitrogen, against a substrate to remove water or other liquid droplets from the substrate.
Yet another object of the present invention is to provide a multi-nozzle gas spray arm for drying liquid from a substrate and preventing the formation of water or liquid spots on the substrate.
A still further object of the present invention is to provide a multi-nozzle gas spray arm which combines a high-pressure, narrow gas stream with a lower-pressure, diffuse gas stream to facilitate effective drying of a substrate surface.
In accordance with these and other objects and advantages, the present invention is directed to a multi-nozzle gas spray arm for a spin coating apparatus, which multi-nozzle gas spray arm in a typical embodiment comprises a primary spray arm and a secondary spray arm which is confluently connected to the primary spray arm. The primary spray arm ejects a narrow, relatively high-velocity nitrogen stream against a substrate while the secondary spray arm ejects a diffuse, relatively low-velocity nitrogen stream against the substrate as the gas spray arm is typically swept across the surface of the wafer. The diffuse nitrogen flow characteristic of the nitrogen ejected from the secondary spray arm is effective in eliminating water and chemical droplets which otherwise would tend to remain and form dry spots on the wafer surface.